1. Field of the Invention
This invention relates to a structure to be grasped applicable to a member which is to be grasped by a grasping device at a set of two projecting portions formed on and projecting from a body portion of the structure.
2. Description of the Related Art
When, for example, a member is to be mounted on another member by an automatic assembling apparatus, a grasping device, mounted on a distal end of a robot arm or an actuator of the automatic assembling apparatus, grasps or grips the member with a pair of grasping portions thereon. In this grasping state the robot arm or the like is operated so as to mount this member on another member.
One example of such a member is one that includes a cylindrical body portion, and a set of two projecting portions which are formed on and project from one end surface of the body portion, and also extend outwards radially from the body portion. For mounting this member on another (other) member, positioned at the opposite end of the body portion to the end on which the set of two projecting portions formed, there are occasions when the set of two projecting portions are grasped by a grasping device.
Here, there is no problem when the set of two projecting portions have the same shape. However, complications arise, when the set of two projecting portions are different in shape from each other, so as to meet functional requirements. Here, since the grasping portions of the grasping device and the projecting portions need to contact each other at least at two surfaces, so that the projecting portions will not move relative to the grasping portions, the set of two grasping portions of the grasping device must be formed respectively into different shapes according to the shapes of the corresponding projecting portions.
An inefficient structure to be grasped, will be specifically described with reference to FIG. 13. A member 200 has a set of two rectangular plate-like projecting portions 204 and 206 formed on a cylindrical body portion 202 and projecting from an end surface thereof. The projecting portions 204 and 206 are disposed on an imaginary straight line L3 coinciding with a diametrical line of the body portion 202, and are elongated along the imaginary straight line L3 when viewed from above. To meet functional requirements, the projecting portions 204 and 206 have different thicknesses (widths) t4 and t5 (≠t4) in a direction perpendicular to the imaginary straight line L3. Therefore, in a grasping device for grasping the member 200 at the set of two projecting portions 204 and 206 thereof, grasping recesses 208A and 210A, formed respectively in a set of two grasping portions 208 and 210, have respective widths of w4 and w5 (≠w4), corresponding respectively to the thicknesses t4 and t5. With this construction, the member 200, when grasped by the set of two grasping portions 208 and 210, will not rattle or displace relative thereto.
In this structure to be grasped, however, the degrees of freedom for the rotational position of the member 200 relative to the grasping device is low. Namely, in a case where the set of two projecting portions 204 and 206 have the same shape (and hence have the same width), there exist two graspable positions per rotation of the member 200 about the axis of the body portion 202 (where the grasping portions 208 and 210 can grasp the member 200). However, with this structure in a case where the set of two projecting portions 204 and 206 are different in shape from each other, the projecting portion 206 can not be fitted into the grasping recess 208A, and therefore there exists only one graspable position per rotation of the member 200. Therefore, the ease of assembly of member 200 on another member using an automatic assembling apparatus was low.